One of the most desirable superconductor materials is niobium-tin (Nb.sub.3 Sn) because of its almost zero resistance at low temperatures. However, it is an extremely hard and brittle material and it is difficult to work with in achieving appropriately shaped and dimensioned wires or rods without discontinuity or other damage.
In order to form the wires and rods, the superconductor materials must undergo repeated compression, drawing, elongation and heating. All of such steps are however detrimental to the integrity, structure and superconducting capability of the niobium-tin material. It has accordingly been the practice to initially perform all of the compression, drawing, forming, elongation, heating and general material working with the pure, ductile, malleable, generally easily workable niobium and copper materials (the latter being used as a highly conductive substrate material). Thereafter, the less workable tin is plated or otherwise adhered to the formed rod or wire surfaces and the entire material is finally heated. Upon such heating, the tin migrates through the conductive copper substrate material to which it has been bonded, and into contact with the contained niobium, to form the requisite niobium-tin material of appropriate dimension and form, in situ.
In the bronze process, Nb rods are inserted into a drilled bronze (Copper 14% tin alloy) billet. This is evacuated, extruded and drawn into hexagonal cross section rods that are restacked into a second extrusion can. This is extruded and drawn to the final wire size and heat treated to diffuse the tin from the bronze matrix to the Nb to form Nb.sub.3 Sn.
The disadvantages of this process are the limited amount of tin available in the matrix and the bronze work hardens quickly and must be annealed every few die passes (about every 40% area reduction or less).
Alternatively, composite conductors can be made by combining the Nb, Cu and Sn in a billet. However, the composite billet can only be cold worked. This permits only limited bonding in the later stages of processing of the copper to copper and the copper to niobium. Such an unbonded conductor is more difficult to process and restricts the latitude one has in the billet configuration.
In accordance with the foregoing, it is an object of the present invention to provide a method for preparing a multifilamentary Nb.sub.3 Sn superconductor, which enables the diffusion bonding of all the components prior to insertion of the tin or tin alloy which is subsequently reacted to form the Nb.sub.3 Sn.
It is a further object of the invention to provide a method for producing a multifilamentary superconductor containing niobium-tin (Nb.sub.3 Sn), in which multiple symmetrically distributed channels are created in a fully bonded niobium-copper billet, for insertion of tin or tin alloy; and wherein no rebundling of components is required as would result in an unbonded composite.